Along with the economic development, technical progress, and improvement of people's living standards, the electrical appliances in residents' houses increase in number, and so the outlets used increase in number. The structure of a normal outlet normally includes the case and the electrodes in the case, which are made of a metal material to match the plug pins. Socket holes are provided on the case at the positions corresponding to the electrodes.
Along with technical developments, the functions of outlets are more varied, and the need for safety becomes higher and higher. An example of such outlets is the GFCI, i.e. a grounding fault circuit interrupter, which has increasingly more applications. A normal GFCI is composed of a base, upper cover with socket holes, leakage signal detection circuit, electromagnetic tripping device that acts under the control of the said leakage signal detection circuit, contact head assembly, grounding assembly, power input connection assembly, and load connection assembly, etc. A GFCI power input connection assembly and load connection assembly are both provided with conductive terminal lugs. The conductive terminal lugs are inserted on the side inner walls of the base. At the positions on the side inner walls of the base corresponding to the conductive terminal lugs, notches are provided to expose the conductive terminal lugs. Therefore, a GFCI can provide loads with a power supply not only through the socket holes on the upper cover, just like a traditional outlet, but also through the load connection assembly. A GFCI can also provide protection in case of electrical leakage in the loads connected with the outlet.
However, for either of the traditional or GFCI outlets, hidden danger exists because the socket holes are open. Due to curiosity, children often poke the socket holes with objects. If the objects are made of conductive material, a casualty accident may occur in all probability.
For this reason, some outlets with safety gate devices have been developed over the years, for example, U.S. Pat. No. 7,312,963. However, the structure of the safety gate device socket is quite complicated. In addition, the safety gates of the example structure have poor universality. They are only applicable to rated current outlets of 15 A or lower, i.e. the planes of the two live plug pins are parallel. The safety gates are not applicable to the outlets with a rated current of 20 A or above. This is because the two live socket holes of the same group of socket holes in an outlet with a rated current of 15 A or below are a pair of long slots provided in parallel, while in an outlet with a rated current of 20 A or above, the planes corresponding to the two live pins of the plug are perpendicular with each other. Therefore, in an outlet with a rated current of 20 A or above, a live socket hole in each group of socket holes is T-shaped, simultaneously matching the plugs with a rated current of both 15 A or below and 20 A or above. However, an outlet with a corresponding safety gate structure is not available up to now.